Side bearing for a railroad car bogie?

Not sure what it is. But in this country it's called a "truck," not a bogie.

I am pretty sure that the top round thing is a side bearing that drops into the top of the truck.  When the truck turns or pivots it rubs up against the truck bolster to allow smooth turning...

Marty

The round cylinder shape is a steel  roller bearing that goes into a roller cage probably Stucki, the rectangular steel casting seams to be a constant contact side bearing that also goes into a rectangular cage, cages were welded or bolted to truck bolster at the side bearing locations.

Both the Stucki roller type side bearing assembly and constant contact side bearing assembly is the point of contact between the car body bolster and truck bolster, both of these side bearing assemblies are mounted 25 inches longitudinal(across the top of the truck bolster), if my memory is correct their is a 3/16 to 1/4 inch gap between the plated welded to the car body bolster and the steel roller/steel casting in their respective cages mounted to the truck bolster.

The lateral rock and roll carbody roll is reacted by force transfer at these side bearing locations from the car body bolster contacting the side bearing assembly which transfers this loads to the truck bolster that bears on damped spring nest between the truck bolster and truck side frame, this force is then transferred by the side frame to the two wheel axles per truck and finally to the rails by the wheels.  Note, freight car bodies have large torsional stiffness, if the car rolls to the left both car bolsters roll to the left contacting the truck bolsters through the side bearing assembly, likewise if the car rolls to the right the car body bolsters rotate to the right contacting the truck bolsters through the side bearing assembly. Additional information there are two side bearing assemblies mounted to the truck bolster,one 25 inches to the left of the bolster center the other 25 inches to the right of the bolster center. the bolster center and the transverse center line of the car coincide.

Referring back to your picture the rectangular casting with the hollow center, this still seams to be a side bearing casting but somewhat large for a freight car, more than likely it is either a side bearing casting for a diesel locomotive or possibly for a heavyweight passenger cars. Also the rectangular constant side bearing blocks that I saw in freight car service where a solid block with no holes. 

There is another issue that can occur under specific conditions such as  worn wheels/track, track curvature, truck centers of cars, loaded/unloaded car. severe wheel flanging, lubrication of track, etc., and side bearing type roller or constant contact could influence the trucks freedom to rotate in curves or retard this rotation. 

Thank you all for the replies. In nearby Raceland, Kentucky, the car shops built various cars. Would a coal car take larger bearing? Sorry about the bogie term, I'm from Eastern Kentucky USA so we call them trucks too. My google research lead me to the term of bogie. 

If you were in England, bogie would be fine!